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From: Peter Maydell <peter.maydell@linaro.org>
Date: Fri, 16 Nov 2018 14:53:16 +0000
Message-ID: <CAFEAcA9va2QarkMFPWNMf43u_GRDoajM-=E0dwinVEgaqRgjHQ@mail.gmail.com>
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Subject: Re: [Qemu-devel] [PATCH v7 03/12] target/arm: Swap PMU values
 before/after migrations
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To: Aaron Lindsay <aaron@os.amperecomputing.com>
Cc: "qemu-arm@nongnu.org" <qemu-arm@nongnu.org>, Alistair Francis <alistair.francis@xilinx.com>, Wei Huang <wei@redhat.com>, Peter Crosthwaite <crosthwaite.peter@gmail.com>, Richard Henderson <richard.henderson@linaro.org>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Michael Spradling <mspradli@codeaurora.org>, Digant Desai <digantd@codeaurora.org>, Aaron Lindsay <aclindsa@gmail.com>

On 5 November 2018 at 18:51, Aaron Lindsay <aaron@os.amperecomputing.com> wrote:
> Because of the PMU's design, many register accesses have side effects
> which are inter-related, meaning that the normal method of saving CP
> registers can result in inconsistent state. These side-effects are
> largely handled in pmu_op_start/finish functions which can be called
> before and after the state is saved/restored. By doing this and adding
> raw read/write functions for the affected registers, we avoid
> migration-related inconsistencies.
>
> Signed-off-by: Aaron Lindsay <aclindsa@gmail.com>

> --- a/target/arm/machine.c
> +++ b/target/arm/machine.c
> @@ -604,6 +604,8 @@ static int cpu_pre_save(void *opaque)
>  {
>      ARMCPU *cpu = opaque;
>
> +    pmu_op_start(&cpu->env);
> +
>      if (kvm_enabled()) {
>          if (!write_kvmstate_to_list(cpu)) {
>              /* This should never fail */
> @@ -625,6 +627,20 @@ static int cpu_pre_save(void *opaque)
>      return 0;
>  }
>
> +static int cpu_post_save(void *opaque)
> +{
> +    ARMCPU *cpu = opaque;
> +    pmu_op_finish(&cpu->env);
> +    return 0;
> +}
> +
> +static int cpu_pre_load(void *opaque)
> +{
> +    ARMCPU *cpu = opaque;
> +    pmu_op_start(&cpu->env);
> +    return 0;
> +}
> +
>  static int cpu_post_load(void *opaque, int version_id)
>  {
>      ARMCPU *cpu = opaque;
> @@ -672,6 +688,8 @@ static int cpu_post_load(void *opaque, int version_id)
>      hw_breakpoint_update_all(cpu);
>      hw_watchpoint_update_all(cpu);
>
> +    pmu_op_finish(&cpu->env);
> +
>      return 0;
>  }

This will end up calling pmu_op_start() and pmu_op_finish()
even if the guest is running KVM and we're not using the
TCG code. Is that what you intended?

thanks
-- PMM